1. Field of the Invention
The present invention relates to a deformable intraocular lens which is inserted into the eye in place of the natural lens when the latter is physically extracted because of cataracts.
2. Description of the Related Art
It is generally accepted that when a cataract-impaired lens is surgically extracted, smaller incisions in the eyeball cause less chance of postoperative astigmatism.
Accordingly, a technique called KPE (Kelman's pharmacoemulsification; suction of lens substance crushed by ultrasonic emulsification) using an ultrasonic emulsification/suction apparatus has been developed. With this apparatus, an opaqued lens is crushed and emulsified by ultrasonication, and then sucked for removal. This technique permits an operation in which lenses are extracted through a small incision of approximately 4 mm, as compared to larger incisions of about 10 mm according to the conventional ECCE operation technique (extracapsular cataract extraction).
In connection with the technique which made small incisions possible as mentioned above, intraocular lenses which can be inserted through a small incision have been developed. Conventional intraocular lenses have an optical part made of a hard material such as glass or plastic, and therefore, the incisions prepared at the time of transplant are greater than the diameter of the optical part which are in most cases 6.5 mm or more. Accordingly, even though a lens is extracted through a small incision according to the KPE technique, it is necessary that the incision be enlarged when a hard intraocular lens is inserted.
To solve this problem, Japanese Patent Application No. S58- 18005 (Japanese Patent Application Laid-open (kokai) No. 146346/1983 Japanese Patent Publication No. H5-58748) discloses a deformable intraocular lens which can be inserted through a small incision made in an eyeball. As shown in FIG. 4 (Prior Art), such an intraocular lens is composed of an optical part 3 made of an elastic material and having predetermined memory characteristics and a plurality of supports 4 which hold the optical part within the eye and which are made of a different material from the optical part 3. Anchors of the supports 4 are embedded in the optical part 3 for bonding the supports to the optical part.
The optical part 3 can be deformed by rolling, bending, extending or folding to reduce its size. Therefore, an intraocular lens having such an optical part can be inserted through a small incision prepared in the eyeball with a newly developed inserting device which can deform the optical part. With this inserting device, the intraocular lens can be inserted through a small incision of about 4 mm in diameter, and can be restored to its original larger shape within the eye, based on the memory characteristics of the optical part 3. Thus, neither the size of the intraocular lens itself nor the method of inserting the lens requires the creation of a large incision.
The above-described deformable intraocular lens according to the prior art involves a drawback that the optical part 3 tends to deviate within the eye. When the supports 4 support the deformable optical part 3 within the eye, they are deformed by external force such as compression force, tensile force, etc., and stress such as compression stress generated in the supports 4 are transmitted to the optical part 3 to generate strains or deformation in the areas 3a of the concave lens shown by the chain lines in FIG. 4, which areas are close to the positions at which the anchors 4a of the supports 4 are embedded.